1. Field of the Invention
The present invention relates to devices and methods, such as those employed in image forming devices, that include a fixing device that fixes an image forming substance, such as toner, to a recording sheet, such as paper or an overhead projection film, for example, so as to make a recorded image on the recording sheet. More particularly, the present invention relates to devices and methods that include a cleaning web that cleans residual image forming substance on the fixing device and in some circumstances also applies a light coat of oil to the fixing device.
2. Discussion of the Background
Conventional image forming devices include a fixing device that fixes toner on a recording sheet, where the toner is arranged in a pattern that corresponds with an original image. In order to fix the toner to the recording medium, the recording medium is passed through a fixing device, which heats and applies pressure to the toner on the recording sheet, so as to permanently affix the toner to the recording sheet.
FIG. 1 shows an example of one type of conventional fixing device that includes a web 4 for cleaning a heat roller 1 during a copying operation. The conventional apparatus includes a heating element 3 contained in the heat roller 1. The heating element 3 is controlled by a basic controller 11 as shown. A press roller 2, is placed in press contact with the heat roller 1, and rotated in an opposite direction to the heat roller 1, as shown by the arrow in FIG. 1. A recording paper may be passed between the respective rollers 1 and 2, in which heat from the heater 3, and pressure from the press roller 2, combined to fix the toner to the recording sheet. The recording sheet then is exited from the image forming apparatus. However, some of the toner "T" remains on the heat roller 1, and unless removed, will adversely effect image quality and perhaps damage the heat roller 1 as will be discussed.
Under control of the basic controller 11, the web 4, which is payed out from a pay-out roller 6, is brought into contact with the surface of the heat roller 1, so as to clean the residual toner from the surface of the heat roller 1. The tension roller 9 is biased by a spring toward the surface of the heat roller 1 so as to keep the web 4 in contact with the heat roller 1. The take-up roller 8, is actuated by a motor 7 under control of the basic controller 11 so as to pull the web 4 during the copy mode of operation.
In the conventional apparatus, the web 4 is used only during a cleaning operation (which occurs during the copying operation) to avoid exhausting the entire supply of the web 4 in too rapid a period of time. Moreover, as the toner is applied against the heat roller 1 only during the copying operation, the conventional approach is to operate the movement of the web 4 only during the copying operation. To this end, the basic controller 11 is programmed to actuate the motor 7 to drive the take up roller 8, and pull the web 4 from the pay-out roller 6 during the copying mode of operation.
Japanese Application JP 59-84274, is an example of such a conventional device where a control circuit controls the motion of a web and moves the web only during a light exposure process (i.e., an image forming, or copying, process). Moving the web for only this period of time is explained in JP 59-84274 as a way of avoiding the wasteful feeding of the web and to extend the replacement period of the web.
Japanese Application JP 6-186874 is directed to a fixing device that after a predetermined number of fixing operations applies a releasing agent to the fixing roller while the temperature of the fixing roller is restored to a predetermined temperature. Driving a web in such a device is not synchronized with the application of the releasing agent.
Another conventional apparatus is disclosed in Japanese Application JP 57-141553 and first detects a temperature of a fixing roller, and operates only when the heat roller is above a predetermined temperature, but not below a predetermined temperature so as to avoid the unnecessary consumption of the web.
The present inventor identified that a failure mechanism of conventional fixing devices, is that a separation layer (such as a non-stick, TEFLON layer) applied to a heating roller can be damaged unless the roller is cleaned in the contact area and the area adjacent to where the web contacts the heat roller 1. Moreover, in reference to FIG. 7, a heat roller 1 is shown to be brought into contact with the web 4, in a nip portion "N". Because the greatest force of the press roller 9, as applied to the heat roller 1, occurs at a central portion, see the dashed line in FIG. 7, residual toner, dust and other potential contaminating materials "W" collect at the edge of the nip portion N and continue up to the center of the nip portion N. However, if after the copying operation this material is not removed, the present inventor has determined that the impurities "W", adhere strongly to the heat roller 1, particularly when the heat roller 1 cools, perhaps after the copying operation, or if another event such as a paper jam or other problem occurs. Furthermore, if the material "W" stays on the heat roller 1 for an extended period of time, even if the heat roller 1 does not reduce in temperature, the attaching force of the material "W" to the heat roller 1 becomes excessive. Consequently, during a subsequent web moving operation, the material "W," which is to the separation layer of the heat roller 1, causes the portion of the separation layer that is in contact with the material "W" to tear-off. As a consequence, the heat roller 1 becomes damaged and subsequently performs poorly in future fixing operations. The symptom experienced is that the material "W", sticks to the recording medium and results in poor adhesion of toner onto the recording medium.